;; Snake Game
(require 2htdp/image)
(require 2htdp/universe)

;; Honors Lecture 10/3/2013

;; SNAKE WORLD
;;
(define-struct world (snake food))
(define-struct snake (dir segs))
;; A World is (make-world Snake Food)
;; A Food is a Posn 
;; A Snake is (make-snake Direction Segs)
;;    Snake must contain at least one segment
;;    The head is the first seg in the list

;; A Segs is one of:  ; Note: Segs is a list of Posns! 
;; - empty
;; - (cons Posn Segs)

;; food and seg positions are in grid coordinates

;; A Direction is one of: 
;; - 'up
;; - 'down
;; - 'left 
;; - 'right

;;;;;;;;;;;;;;;;;;;;
;; Templates

#;(define (world-temp w)  ; todo
  ... )

#;(define (food-temp f)   ; todo
  ... )

#;(define (snake-temp snk)
  ... (snake-dir snk) ... (snake-segs snk))

#;(define (segs-temp segs)
  (cond [(empty? segs) ...]
        [else ... (first segs) ... (segs-temp (rest segs)) ...]))
  
#;(define (direction-temp dir)
  (cond [(symbol=? dir 'up) ...]
        [(symbol=? dir 'down) ...]
        [(symbol=? dir 'left) ...]
        [(symbol=? dir 'right) ...]))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Initial wish list: 

;; world->scene : World -> Image
;; food+scene : Food Image -> Image
;; snake+scene : Snake Image -> Image

;; snake-move : Snake -> Snake
;; snake-grow : Snake -> Snake

;; world->world : World -> World
;; key-hndlr : World KeyEvent -> World

;; eating? : World -> Boolean
;; game-end? : World -> Boolean
;; self-collide? : Snake -> Boolean
;; wall-collide? : Snake -> Boolean

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; CONSTANTS: things we need to keep track of that never change

(define GRID-SQSIZE 10) ; width of a game-board square
(define BOARD-HEIGHT 20) ; height of board in grid squares
(define BOARD-WIDTH 30) ; width of board in grid squares
(define BOARD-HT/PIX (* GRID-SQSIZE BOARD-HEIGHT))
(define BOARD-WD/PIX (* GRID-SQSIZE BOARD-WIDTH))

(define BACKGROUND (empty-scene BOARD-WD/PIX BOARD-HT/PIX))

(define TICK-RATE 0.3) 

(define SEGMENT-RADIUS (quotient GRID-SQSIZE 2))
(define SEGMENT-IMAGE (circle SEGMENT-RADIUS 'solid 'red))
(define FOOD-RADIUS (floor (* 0.9 SEGMENT-RADIUS)))
(define FOOD-IMAGE (circle FOOD-RADIUS 'solid 'green))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Example data

(define Food1 (make-posn 5 3))
(define Snake1 (make-snake 'left (cons (make-posn 6 10) empty)))
(define World1 (make-world Snake1 Food1))

(define Snake2 (make-snake 'left (cons (make-posn 5 3) empty)))
(define World2 (make-world Snake2 Food1)) ; an eating scenario

(define Food3 (make-posn 10 20))
(define Snake3 
  (make-snake 'left 
              (cons (make-posn 5 3) 
                    (cons (make-posn 6 3) empty)))) ; 2-segment snake
(define World3 (make-world Snake3 Food3))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;



;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Image/scene painting functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; todo: world->scene, food+scene, snake+scene, other helpers...



;; Examples/Tests: scene-painting functions


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Snake motion and growth
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; snake-move : Snake -> Snake
;; Move the snake by one step in the current direction
(define (snake-move snk)
  (make-snake (snake-dir snk) 
              (move-segs (snake-segs snk) (snake-dir snk))))

;; A NESegs (non-empty segments) is one of: 
;; -- (cons Posn empty)
;; -- (cons Posn NESegs)

;; move-segs : NESegs Direction -> NESegs
;; Move the snake's segments by one step
;;  How: new head is old head moved by one step in approp direc
;;       new tail is old segs minus last
(define (move-segs nesegs dir)
  (cons (move-seg (first nesegs) dir)
        (segments-all-but-last nesegs)))
  
;; segments-all-but-last: NESegs -> Segs
;; remove the last segment in the list 
(define (segments-all-but-last nesegs)
  (cond [(empty? (rest nesegs)) empty]
        [else (cons (first nesegs) 
                    (segments-all-but-last (rest nesegs)))]))

;; move-seg : Posn Direction -> Posn
;; move the segment in the given direction
(define (move-seg p dir)
  (cond [(symbol=? dir 'up) 
         (make-posn (posn-x p) (add1 (posn-y p)))]
        [(symbol=? dir 'down) 
         (make-posn (posn-x p) (sub1 (posn-y p)))]        
        [(symbol=? dir 'left) 
         (make-posn (sub1 (posn-x p)) (posn-y p))]
        [(symbol=? dir 'right) 
         (make-posn (add1 (posn-x p)) (posn-y p))]))

;; snake-grow : Snake -> Snake
;; Grow snake one step
;; This is just like snake-move except we don't drop last seg
(define (snake-grow snk)
  ...)

;; eat&grow : World -> World
;; Eat the current food, grow the snake and produce new food
(define (eat&grow w)
  ...)

;; Examples/Tests for snake movement and growth
(check-expect (segments-all-but-last 
               (cons (make-posn 6 10) empty))
              empty)

(check-expect (segments-all-but-last 
               (cons (make-posn 5 10) 
                     (cons (make-posn 6 10) empty)))
              (cons (make-posn 5 10) empty))

(check-expect (move-seg (make-posn 6 10) 'up)
              (make-posn 6 11))
(check-expect (move-seg (make-posn 6 10) 'down)
              (make-posn 6 9))
(check-expect (move-seg (make-posn 6 10) 'left)
              (make-posn 5 10))
(check-expect (move-seg (make-posn 6 10) 'right)
              (make-posn 7 10))

(check-expect (snake-move Snake1)
              (make-snake 'left 
                          (cons (make-posn 5 10) empty)))
  
#;(check-expect (snake-grow Snake1)
              (make-snake 'left
                          (cons (make-posn 5 10)
                                (cons (make-posn 6 10) empty))))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Collision detection
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; todo: eating?, self-collide?, wall-collide?, helpers...


;; Examples/Tests for collision functions

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; todo: world->world, key-handler, game-end?, 


#;(big-bang World1
          (to-draw world->scene)
          (on-tick world->world TICK-RATE)
          (on-key key-handler)
          (stop-when game-end?))